A turbomachine, for example a jet engine, generally comprises a fan, one or more compressor stages, a combustion chamber, one or more turbine stages and a nozzle. The gases are driven by rotors of the fan, of the compressor and of the turbine, thanks to radial impeller blades fixed to the periphery of the rotors.
The concept of an internal, external, radial, upstream or downstream position or arrangement is defined relative to the main axis of the turbomachine and in the direction of flow of the gases in the latter.
A moving turbine impeller blade comprises a foot, by which it is fixed to the rotor disk, a platform, forming one element of the internal wall delimiting the gas artery, and a blade, which extends globally along a radial axis and is swept by the gases. Depending on the motor and the turbine stage, the blade ends, at its end remote from the foot, in an element transversal to the general (main) axis of the blade, called heel, which forms one element of the external wall delimiting the gas artery.
The external surface of the heel supports one or more radial plates—or tabs—adapted to form, with the facing stator wall, a labyrinth seal, ensuring gas-tightness; to this end, said stator wall is generally formed by a ring made of abradable material, on which the plates rub. The plates comprise an upstream face and a downstream face which extend transversely to the flow of gas.
The impeller blade can be of monoblock construction, the foot, the platform, the blade and the heel being formed of a single piece. The impeller blade is formed by molding, by a so-called “lost wax” method, well known to those skilled in the art. In such a method:                a model of the impeller blade is previously formed in wax;        this model is dipped in a slip of refractory ceramic material which, once baked, forms a shell;        the wax is melted and evacuated, leaving a “shell mold” formed of the ceramic material, and whose internal volume defines the shape of the impeller blade;        molten metal is introduced into the shell mold, a plurality of shell molds generally being assembled in a cluster with a common supply of metal;        the shell mold is broken, leaving the metal impeller blade.        
The metal supply points of the shell mold generate, on the metal impeller blade formed in the mold, metal pilot points, relatively thick, that must be machined once the impeller blade is formed. The supply is generally at the level of the heel of the impeller blade. The diameter of the supply duct, and consequently of the heel formed, is great, even though this supply is close to the plates of the labyrinth seal, which are of low thickness; there follows, if just one supply is provided, a poor distribution of the metal in the shell mold, leading to problems of porosity of the impeller blade, in particular at the level of its plates.
This problem can be resolved by providing two supply inputs, the diameter of the supply ducts being reduced accordingly. Thus, instead of a high diameter supply, two low diameter supplies, but distant from each other, are provided, which provides for a better distribution of the metal and avoids the problems of porosity.
Nevertheless, it would be desirable to resolve the problems of porosity while keeping a single supply.